Olefin oxides, as for example propylene oxide, are amongst the most important chemicals widely used for the preparation of various textiles and plastics. Several studies have intensively attempted to search for a process to obtain an olefin oxide with a high production rate hoping for an economically feasible plant design.
Recently, copper-modified catalysts have become attractive for propylene epoxidation [J. Catal. 236 (2005) 401]. A study of a single crystal of metallic copper showed that Cu0 was intrinsically a much more selective epoxidation catalyst for alkenes containing allylic hydrogen than Ag0 [J. Mol. Catal. A 228 (2005) 27]. It has been found that CuI supported on a silica (SiO2) catalyst was also efficient for the epoxidation under oxygen-rich conditions [J. Phys. Chem. C 112 (2008) 7731].
Furthermore, a few lead single-metal modified catalysts have been examined for the direct gas phase epoxidation of propylene such as molybdenum on SiO2 [Appl. Catal. A 316 (2007) 142.; Catal. Lett. 121 (2008) 33] and iron on Mobil Composition of Matter (MCM)-41 [J. Catal. 239 (2006) 105; JJ. Phys. Chem. B 109 (2005) 23500].
Supported multimetallic catalysts for propylene epoxidation have attracted great interest since they often present excellent catalytic properties in comparison to individual metal components [Ind. Eng. Chem. Res. 42 (2003) 1571].
There are some proposed catalysts such as sodium chloride-modified VCexCu1-x mixed oxide [J. Catal. 211 (2002) 552], silver-based catalysts containing nickel metal [Appl. Catal. A 294 (2005) 34], gold on titanium-SBA-15 [J. Catal. 248 (2007) 235], and gold on MCM-41 [Appl. Catal. A 240 (2003) 243].